the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Nov 2025
Large-scale drivers of compounding hot and dry events in three breadbasket regions
Abstract. Compound hot and dry events cause damage to ecosystems and society. While these events have been widely studied individually, their co-ocurrence and the associated large-scale atmospheric drivers remain less understood. Here, we use reanalysis products and observational data to identify compound hot and dry events in the historical period from 1960 to 2020. We analyze the large-scale circulation patterns associated with compound occurrence of hot and dry events when they affect large portions of three breadbasket regions in the Northern Hemisphere, namely North America, Europe and the Mediterranean and eastern Asia. We find that compound hot and dry events recur throughout the historical period and are consistently linked to Rossby wave patterns and mid-tropospheric anticyclonic ridging, which trigger land-atmosphere feedbacks resulting in the reinforcement of the events. Our study highlights that the spatial extent of compound hot and dry events offers a metric for assessing regional impacts.
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Status: open (until 08 Mar 2026)
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CC1: 'Comment on egusphere-2025-5073', Yongli He, 08 Jan 2026
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CC2: 'Reply on CC1', Natalia Castillo, 03 Feb 2026
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1)Â Thanks for your comment. In Figure 5a, we are referring to the total number of COHDEs during high FA events in NA (not a high-low composite differences). The same applies to Figure 6a (EM) and 7a (AS). We will revise the caption of the figure accordingly to avoid ambiguity:
Figure 5. a) Total number of COHDES during high Fraction of Area (FA) events (19 events) in North America (NA, highlighted by the black contours). Composite differences of high FA events minus low FA events in NA: b) maximum daily temperature at 2m (shadings) and isohypses at 500 hPa (z500), c) precipitation (shadings) and isohypses at 500 hPa, d) surface sensible and e) surface latent heat fluxes, f) distribution of the dominant wavenumbers associated with the v250 anomalies, g) meridional component of the wind at 250 hPa (v250) and h) zonal component of the wind at 250 hPa (u250). Hatched areas in the composites indicate regions where differences are statistically significant at the 95% confidence level, based on a Student’s t-test.
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2) Thanks for your comment. This is due to the construction of the composite differences, which are based on events in North America only. Although Figure 5g shows a circumglobal wave train, the anomalies in the variables (precipitation, surface sensible and latent heat fluxes) triggering the compounding of hot and dry conditions are not strong enough in the places where the other ridges are located to trigger more compounding there.
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3) Thanks again for your comment. We were referring to Figure 1, as we describe the methodology in the flowchart and intended to indicate that this is the final step of the workflow. We will revise the manuscript to state this more clearly.
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Citation: https://doi.org/10.5194/egusphere-2025-5073-CC2
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CC2: 'Reply on CC1', Natalia Castillo, 03 Feb 2026
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1. Clarification on Figure 5a I have a question regarding the "High FA minus Low FA" methodology mentioned in the Figure 5 caption. Since the definitions yield different sample sizes (19 vs. 92 events), does a direct subtraction of the "Number of COHDEs" create an unfair comparison? It would be helpful to know if you normalized these counts to account for the unequal sample sizes.
2. Rossby Wave Train vs. Localized Events In Figure 5g, the Rossby wave train is clearly circumglobal. I am curious why the compound events in Figure 5a appear only in North America, while the other ridges in the wave train do not seem to generate corresponding COHDEs elsewhere. Is there a specific physical mechanism dampening the response in other regions, or is this primarily due to the composite being triggered specifically by North American events?
3. Minor Correction I noticed a potential typo in Line 158. The text cites "(Fig. 1)," but based on the context, it seems it should refer to Figure 5a.